Premixed methanol diesel dual fuel (PMDDF) is a combustion mode in which methanol is injected from the intake port and then ignited by the direct injected diesel in the cylinder. Many studies have shown that PMDDF mode has the potential to reduce NOx and PM emissions simultaneously. In this study, investigation on realizing national phase Ⅳ emission standard by using PMDDF combustion mode coupling with diesel oxidation catalyst (DOC) and particulate oxidation catalyst (POC) was carried out on a 6-cylinder heavy-duty diesel engine. The effects of premixed methanol on engine combustion process and fuel economy were also investigated. The experimental results showed that with the engine power keeping unchanged, the emission level of the engine was improved from national phase Ⅲ to Ⅳ by using PMDDF combustion mode and the simple aftertreatment DOC+POC. And the specific fuel consumption almost remained unchanged. This technology provided a new route for the realization of national phase Ⅳ emission standard. In addition, it was also found that the ignition delay of PMDDF combustion mode was prolonged and the combustion duration was shortened with the increase of premixed methanol ratio. At high engine load, the brake specific fuel consumption of PMDDF combustion mode was lower than that of baseline engine, but it was slightly higher at low engine load. Therefore, the premixed methanol ratio can be a little higher at high engine load but can not be very high at low engine load. 